Three years ago, scientists used an Earth-sized telescope to capture the first-ever image of a black hole. Now they’ve done it again – this time, closer to home, and from a very different invisible behemoth.
The Event Horizon Telescope (EHT) has now captured images of two super-heavy black holes: the one at the center of a galaxy called M87 and the one at the center of our own galaxy, the Milky Way† In the process, the hundreds of scientists involved in the endeavor got their first glimpse of two objects that have surprisingly little in common.
“The two images are very similar to us when we look at them in the sky,” Feryal Özel, an astrophysicist at the University of Arizona and a member of EHT’s scientific board, said at a news conference held Thursday by the National Science Foundation. . (May 12) to reveal the new image of Sagittarius A* in the Milky Way. “But the two black holes couldn’t have been more different in practically every other way.”
Sagittarius A* in photos: The discovery of the black hole in the Milky Way in images
In particular, the two black holes differ in how difficult it is to image material moving around its boundary, or event horizon† (That material, which glows when consumed, is what lights up the faint rings that the EHT was supposed to produce, since black holes don’t emit light themselves.)
Wisely, the EHT took on the less challenging target first. That’s the monster hiding in M87, also known as M87*. This black hole is, of course, farther from Earth, but it is also much larger and material moves at a slower pace around the event horizon.
“Material swirls around M87* over many days,” Vincent Fish, an astrophysicist at the Massachusetts Institute of Technology’s Haystack Observatory and member of EHT’s scientific board, said during the news conference. “He sits still for his picture.”
The Milky Way’s supermassive black hole, called Sagittarius A*, is less cooperative. “It only takes a few minutes for material to move close to the horizon of Sagittarius A* because it is much smaller,” added Fish. “It changes quickly, so we had to collect our data quickly.”
And Sagittarius A*’s challenge was apparent when scientists analyzed the data the EHT also collected. Katie Bouman, a computer scientist at the California Institute of Technology and co-leader of the EHT Imaging Working Group, said at the press conference that when the independent imaging teams formed to analyze the M87* results compared their first shots on an image , they were more or less the same.
Not so for the second black hole. “Imaging Sagittarius A* was a bit more messy than imaging M87*,” Bouman said. This time, the imaging groups were hesitant to produce an initial image because there was so much less consensus among the team members.
While the material surrounding Sagittarius A* moves clumsily across the event horizon, our supermassive black hole nevertheless offers a much tamer surface environment than M87*. The turbulence in this region is determined by the black hole’s appetite, which varies despite the popular belief that all black holes gulp with the suction of a cosmic vacuum cleaner.
“If Sagittarius A* were a person, he would consume a single grain of rice every million years,” Michael Johnson, an astrophysicist at the Harvard/Smithsonian Center for Astrophysics and member of the EHT Science Board, said during the news conference. “Only a trickle of material actually reaches the black hole.”
Sagittarius A* grows at that slow rate and is quite a graceful eater. “That’s why the environment is relatively soft,” Özel said. “Obviously, when we say that, the temperatures and magnetic field strengths are still quite high, and the movement of gas around it is still turbulent.”
But while Sagittarius A* was the harder target for EHT scientists to study, it was also a significant challenge to tackle, the scientists said. “Sagittarius A* gives us a glimpse into the much more standard state of black holes: still and calm,” Johnson said. “M87 was exciting because it was extraordinary. Sagittarius A* is exciting because it is common.”
But despite all the differences, the new portrait of Sagittarius A* can even be mistaken for the iconic image released in 2019 at a glance.
“If we look at the heart of each black hole, we find a bright ring around the black hole’s shadow,” said Özel. “These two images are similar in that they are the result of fundamental gravity.”
That’s physics, though it’s still tempting to have fun with the resemblance. “Spacetime, the fabric of the universe, wraps around black holes in exactly the same way, regardless of their mass or what surrounds them,” Özel said. “Looks like black holes love donuts.”
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